Magnetic Resonance Study of Bulky CVD Diamond Disc

At a Glance

Metadata	Details
Publication Date	2024-04-18
Journal	Materials
Authors	Alexander I. Shames, A. M. Panich, Lonia Friedlander, Haim Cohen, J. E. Butler
Institutions	Ariel University, Ben-Gurion University of the Negev
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: Magnetic Resonance Study of Bulky CVD Diamond Disc

Executive Summary

This documentation analyzes the structural and spectroscopic findings of a thick, sizable Polycrystalline CVD Diamond (PCD) disc, focusing on defect characterization via advanced magnetic resonance techniques.

Material Profile: The study utilized a bulky PCD disc (50 mm diameter, ca. 560 µm thickness), demonstrating the feasibility of growing substantial CVD diamond components for optical, thermal, and radiation sensing applications.
Defect Inhomogeneity: EPR and ¹³C NMR measurements conclusively revealed significant macro- and micro-inhomogeneity in the distribution of nitrogen-related defects (P1 centers) across the disc volume.
Spin Relaxation Correlation: The ¹³C Spin-Lattice Relaxation Time (T_1n) was found to be inversely proportional to the local paramagnetic defect density (N_s), varying from 2070 s (N_s ~3 ppm) to 1340 s (N_s ~5 ppm).
Structural Quality: XRD confirmed a polycrystalline structure with a strong preferred (111) growth orientation, yielding large crystallites (> 1220 nm) in this direction. Total nitrogen impurity was determined to be < 90 ppm.
Quantum Defect Absence (Key Finding): Crucially, the study revealed no traces of NV^- (W15) centers, even after high-dose e-beam (1 kGy) and gamma (2 MGy) irradiation followed by 850 °C annealing, highlighting the challenge of NV creation in this specific growth recipe.
Methodology: A combination of continuous wave (CW) EPR, Fourier Transform Infrared (FTIR) spectroscopy, Nuclear Magnetic Resonance (NMR), and X-ray Diffraction (XRD) was employed for comprehensive material characterization.

Technical Specifications

The following hard data points were extracted from the analysis of the bulky CVD diamond disc:

Parameter	Value	Unit	Context
Sample Diameter	50	mm	Polycrystalline CVD Disc
Sample Thickness	ca. 560	µm	Bulk material requirement
Total Nitrogen Content	< 90	ppm	Estimated via FTIR (A-centers and C-centers)
Total Primary Defect Content (N_s)	2.3 to 4.9	ppm	Sample-dependent variation (macro-inhomogeneity)
P1 Center Content (N_s)	0.6 to 1.1	ppm	Substitutional Nitrogen
¹³C Spin-Lattice Relaxation (T_1n)	2070 ± 79	s	Measured in low-defect region (N_s ~3 ppm)
¹³C Spin-Lattice Relaxation (T_1n)	1340 ± 126	s	Measured in high-defect region (N_s ~5 ppm)
Preferred Growth Orientation	(111)	N/A	Strong preferred orientation (XRD)
Crystallite Size (111 direction)	> 1220	nm	Calculated via Scherrer formula
Crystallite Size (220 direction)	4 to 90	nm	Range observed depending on sample tilt

Key Methodologies

The CVD diamond disc was synthesized using a two-stage MPCVD process, followed by post-growth treatments for defect transformation studies.

Growth System: Home-built Microwave Plasma CVD (MPCVD) system utilizing a 5 kW microwave source operating at 2.45 GHz.
Substrate: Molybdenum (Mo) substrate with a water-cooled holder.
Nucleation Phase (60 h):
- Pressure: 115 torr
- Temperature: 836 °C
- Gas Flows: H₂ (500 sccm), CH₄ (18 sccm), O₂ (0.5 sccm)
Growth Phase (56.55 h):
- Pressure: 115 torr
- Temperature: 836 °C
- Gas Flows: H₂ (478 sccm), CH₄ (20 sccm), O₂ (2.0 sccm)
Post-Processing (Irradiation & Annealing):
- E-beam Irradiation Dose: 1 kGy
- Gamma Irradiation Dose: 2 MGy
- Annealing: 850 °C for 2 hours in a vacuum environment.
Characterization Techniques: Continuous Wave (CW) EPR (X-band), ¹³C and ¹H Solid-State NMR (8.0 T), FTIR spectroscopy (500-4000 cm^-1), and Bragg-Brentano XRD (Cu Kα radiation).

6CCVD Solutions & Capabilities

The research demonstrates the critical role of precise defect control and material homogeneity in achieving desired diamond properties. 6CCVD is uniquely positioned to supply the high-quality, customized MPCVD diamond required to replicate, extend, and optimize this research for commercial applications.

Applicable Materials

To replicate or extend this research, particularly focusing on bulk properties and defect engineering, 6CCVD recommends the following materials:

Polycrystalline Diamond (PCD) - Thermal/Mechanical Grade:
- Application: Ideal for high-power thermal management (heat spreaders) and mechanical components, matching the bulk nature of the studied disc.
- Customization: We offer PCD plates/wafers up to 125 mm in diameter, exceeding the 50 mm disc size studied, and thicknesses up to 500 µm (easily meeting the 560 µm requirement).
Nitrogen-Doped PCD (N-PCD):
- Application: For studies requiring controlled P1 center concentration (substitutional nitrogen) and analysis of spin diffusion/relaxation phenomena (T_1n).
- Benefit: 6CCVD can provide N-PCD with specified nitrogen concentrations to minimize the observed macro-inhomogeneity (2.3 ppm to 4.9 ppm variation) noted in the paper.
High-Purity Single Crystal Diamond (SCD):
- Application: For follow-up studies requiring highly ordered structure, minimal grain boundaries, and precise control over defect creation (e.g., creating NV centers via controlled implantation/irradiation).

Customization Potential

The paper utilized a specific geometry (50 mm disc) and highlighted the importance of structural orientation and defect location. 6CCVD offers comprehensive customization services to meet these advanced research needs:

Custom Dimensions & Thickness: We provide plates and wafers in custom dimensions up to 125 mm (PCD) and thicknesses ranging from 0.1 µm to 500 µm (SCD/PCD), including substrates up to 10 mm thick.
Surface Finish: The paper’s findings on structural inhomogeneity necessitate high-quality surface preparation for subsequent processing. 6CCVD guarantees ultra-smooth polishing:
- SCD: Ra < 1 nm
- Inch-size PCD: Ra < 5 nm
Metalization Services: For electrochemical or sensor applications mentioned in the paper’s introduction, 6CCVD provides in-house metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu layers, tailored to specific device requirements.
Structural Control: We can engineer PCD materials to optimize or minimize preferred crystallographic orientations (e.g., (111) or (100)) based on the target application (e.g., maximizing thermal conductivity or minimizing surface roughness).

Engineering Support

The research underscores the complexity of defect engineering, particularly the challenge of creating NV centers in nitrogen-containing CVD diamond. 6CCVD’s in-house PhD team specializes in defect physics and material optimization.

Defect Engineering Consultation: Our experts can assist researchers in designing growth recipes (CH₄/H₂/N₂ ratios, temperature, pressure) to achieve specific defect profiles, whether the goal is high-purity material (low N) or controlled incorporation of P1 centers for spin physics studies.
Quantum Applications: For projects aiming to utilize NV centers (W15), 6CCVD provides SCD materials with ultra-low intrinsic nitrogen content, optimized for subsequent high-fluence irradiation and annealing protocols necessary for efficient NV creation.
Global Logistics: We ensure reliable global shipping (DDU default, DDP available) for sensitive materials, guaranteeing prompt delivery to research facilities worldwide.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Diamonds produced using chemical vapor deposition (CVD) have found many applications in various fields of science and technology. Many applications involve polycrystalline CVD diamond films of micron thicknesses. However, a variety of optical, thermal, mechanical, and radiation sensing applications require more bulky CVD diamond samples. We report the results of a magnetic resonance and structural study of a thick, sizable polycrystalline CVD diamond disc, both as-prepared and treated with e-beam irradiation/high-temperature annealing, as well as gamma irradiation. The combination of various magnetic resonance techniques reveals and enables the attribution of a plentiful collection of paramagnetic defects of doublet and triplet spin origin. Analysis of spectra, electron, and nuclear spin relaxation, as well as nuclear spin diffusion, supports the conclusion of significant macro- and micro-inhomogeneities in the distribution of nitrogen-related defects.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma17081871

References

2022 - Synthesis of Diamonds and Their Identification [Crossref]
2005 - Magnetic resonance study of nanodiamonds [Crossref]
2006 - Processing Quantum Information in Diamond [Crossref]
1988 - EPR in diamond thin films sinthesized by microwave plasma chemical vapor deposition [Crossref]
1996 - Hydrogen-related defects in polycrystalline CVD diamond [Crossref]
1996 - Nitrogen-related dopant and defect states in CVD diamond [Crossref]
1994 - Power saturation and the effect of argon on the electron spin resonance of diamond deposited from a microwave plasma [Crossref]